Green roofs aren’t just isolated islands of nature. They’re also stepping stones for flying insects such as bees, scientists have found.

While it’s clear that green roofs can boost biodiversity in cities, scientists didn’t know whether these patches could act as connected habitat. So a team studied 40 green roofs in Zurich, Switzerland, with plants ranging from succulents to meadow species. From May to September 2010, the researchers caught 48,084 ground beetles, spiders, weevils, and bees from nearly 500 species on the green roofs and at corresponding green spaces on the ground.

The team then looked for links between the arthropod communities and factors such as the size of the roof, the amount of flowers, and distance to the nearest green roof or other habitat. For ground beetles and spiders, the local environment had a big influence on the species present. But for flying bugs such as bees and weevils, “connectivity was by far the most important variable,” the authors write in Ecology.

These roof-hopping insects may help pollinate plants, the team notes. And connected populations are more likely to bounce back from disturbances. — Roberta Kwok | 27 September 2013